AbstractThe level of several glycolytic intermediates, phosphate compounds, and reduced and oxidized pyridine nucleotides was determined in an isolated crustacean nerve cell preparation both at rest and after prolonged physiological stimulation. The glycogen decreased consistently with the lactate increase during impulse activity. ATP showed a continuous decrease during prolonged stimulation while ADP and Pi showed opposite patterns. After stimulation, the ratio TPN/TPNH fell by more than 50 per cent. This was due to a decrease of TPN. Similarly, the DPN/DPNH ratio fell by 50 per cent, but in this case it was due to a decrease of DPN and a simultaneous increase of DPNH. The results strongly suggest the involvement of glycolysis in the mechanism maintaining impulse activity in this neurone. Impulse activity in the crustacean nerve cell is linked to an energy requiring system. This energy is furnished by ATP splitting and glycolysis directly or through the arginine phosphate step supporting the ATP resynthesis.